1. Field of the Invention
The present invention relates to a method of distinguishing disks, and particularly relates to a method of distinguishing a particular type of disk from different types of disks on which signals are recorded in different formats respectively, according to an output from an optical pickup.
2. Description of the Background Art
It is important to make a DVD (Digital Video Disk) reproduction apparatus compatible with CD (Compact Disk) reproduction in view of utilization of abundant soft resources of the CD. Therefore, an art of providing the DVD reproduction apparatus with a compatible CD reproduction function is required.
Regarding the specifications of the CD and the DVD, they are different in the physical specification and the recording signal specification as shown in Table 1 and Table 2, and accordingly switching of the pickup and control thereof corresponding to respective disks are necessary.
TABLE 1 Physical Specification of Disk DVD CD Disk Substrate Thickness (mm) 0.6 1.2 Disk Structure two sheets attached single sheet Minimum Pit Length (mm) 0.4 0.83 Track Pitch (mm) 0.74 1.6
TABLE 1 Physical Specification of Disk DVD CD Disk Substrate Thickness (mm) 0.6 1.2 Disk Structure two sheets attached single sheet Minimum Pit Length (mm) 0.4 0.83 Track Pitch (mm) 0.74 1.6
The disc distinguishing methods interesting to the present invention are disclosed in Japanese Patent Laying-Open Nos. 61-42751 and 3-181062, for example.
According to a conventional method, a disk type is identified by the difference of reflectance for a light beam among recording media such as an optical disk. When disks having nearly the same reflectance such as the DVD and CD are to be distinguished, an allowable error of reference values are small to make it difficult to correctly distinguish them due to variation of an RF signal or the like.
Further, the level of a focus error signal for a dual DVD is low compared with that for a single DVD to be easily subjected to noises of a circuit or the like. Therefore, to physically distinguish between the dual DVD and the single DVD using the conventional method described above is difficult.